The present invention relates to piston and cylinder type shock absorbers, and more particularly, to shock absorbers of the type described that are adapted for use with the seat of a truck or similar motor vehicle and that permit adjustable damping.
In the past, fluid has been allowed to enter and leave the so-called compression chamber and rebound chamber defined or formed in the cylinder of piston and cylinder type shock absorbers, either through the piston or through a passage or passages that provide communication between the chambers in the cylinder and a reservoir. The damping characteristics of such shock absorbers are determined by the rate at which fluid is permitted to enter and leave the chambers of the cylinder. This rate, in turn, controls the speed at which the piston may move in the cylinder responsive to the external forces applied to the shock absorber.
Those working in the art have long recognized the desirability of being able to change or adjust the rate of fluid flow so that the damping characteristics of a shock absorber of this type may be changed to accommodate different, anticipated conditions. Adjustable damping shock absorbers have been proposed in the past and have included mechanisms for selectively changing the rate of fluid flow. These prior mechanisms share the disadvantages of requiring structurally complex individual components, entire mechanisms, or both. The complexity is a result of the need to provide adjustment of the primary fluid flow path of the shock absorber, the inaccessibility of the location of the flow adjustment, and the need to provide for adjustment over a wide range of flows. This complexity results in relatively high fabrication or assembly costs.
Additionally in many of these prior mechanisms, adjustment of the flow rate requires the collapsing of the shock absorber and rotation of the piston against a retaining mechanism. Others require careful adjustment and securing of the mechanism. This need to so manipulate the shock absorber or mechanism control member to adjust the damping characteristics has made these prior shock absorbers not only expensive but difficult to commercialize.
More specifically, these prior proposed adjustable damping shock absorbers have included fluid flow control mechanisms having an externally adjustable member to reduce or restrict the area of an orifice, and thereby control the rate of flow through the orifice. An example of a mechanism for positioning orifice restricting rods within the orifices in a piston and within a reservoir flow passage are described in U.S. Pat. No. 2,780,321.
A reservoir fluid flow control mechanism having a hollow, cylindrical metering pin that is mounted in a larger diameter cylindrical bore is described in U.S. Pat. No. 4,214,737. The pin has a radial passage extending from its side wall to an axial central passage. The pin is eccentrically positioned in the bore so that the pin contacts the bore side wall. The bore includes a side wall opening through which fluid may flow into the bore. Flow into and through the pin is adjustably controlled by rotating the pin in the bore from a fully open position where the pin is positioned opposite the bore side wall opening to a fully closed position where the portion of the pin contacting the bore side wall substantially covers the side wall opening.
Another patented flow control mechanism, described in U.S. Pat. No. 4,164,274, has a cylindrical chamber that includes radial openings communicating with the shock absorber cylinder and reservoir. A valve spool, with annular lands, is disposed in the chamber and is in close slidable contact with the chamber side wall. An externally adjustable assembly is used to axially move the valve spool within the chamber so that the spool valve lands cover and uncover the radial openings.
U.S. Pat. Nos. 3,937,307, 4,043,435, and 4,232,767 several other flow control mechanisms for selectively covering and uncovering fluid flow passages extending through a shock absorber piston. Each mechanism is adjusted by rotating a flat closing member disposed perpendicular to the axis of the piston.
Mechanisms which vary the pressure required to open valves in the fluid passages through shock absorber pistons have also been used to provide adjustable damping for the shock absorbers. A mechanism to vary the height of a coil spring seat of a shock absorber piston valve is disclosed by U.S. Pat. No. 2,788,092. Similarly, U.S. Pat. No. 4,298,102 describes a mechanism for adjusting the height of a valve seat in a passage through a shock absorber piston so as to limit the opening of a flexible valve element.